1. Field of the Invention
The present invention relates to a chip capacitor and a method of manufacturing a chip capacitor.
2. Description of the Related Art
One conventional method of manufacturing a chip capacitor is closed in Japanese patent 3084895. According to the disclosed method, a capacitor component has an anode lead and a sintered body of a metal having a valve action in which the anode lead is embedded so as to project from the embedding surface, the anode lead is placed on a joint tongue bent from an anode terminal, and the joint tongue and the anode lead are welded to each other by a laser beam.
When the joint tongue and the anode lead are welded to each other by the laser beam, because the applied laser beam is reflected from the welded region or the laser beam is applied as a beam spot, the laser beam may be reflected from a region other than the welded region and applied to an irrelevant region. If the reflected laser beam is applied to the capacitor component itself other than the anode lead, then the quality of the capacitor component and hence the quality of the chip capacitor are lowered.
The capacitor component is produced as follows: shaped powdery body of a metal having a valve action with an anode lead mounted thereon is sintered into an anode body, and then a dielectric layer of oxide metal film is formed on the sintered body of the anode body. Then, a cathode conductor layer is formed on the dielectric layer, and thereafter a semiconductor layer is formed on the cathode conductor layer, whereupon the capacitor component is completed. When the semiconductor layer is formed, if the mother liquor of the semiconductor creeps up the anode lead to bring the semiconductor layer into contact with the anode lead, then the capacitor component suffers a large leakage current and loses desired capacitor characteristics. To avoid such a drawback, Japanese laid-open patent publication No. 64-22018 discloses a capacitor in which a water-repellent resin is applied to an embedding surface in which an anode lead of a sintered body is embedded. According to the disclosed capacitor, a reinforcing resin layer is formed on the water-repellent resin for avoiding shortcomings due to mechanical stresses caused when an anode lead of a capacitor component is welded to an anode terminal by electric resistance welding.
If the capacitor component having the water-repellent resin and the reinforcing resin layer is applied to a laser beam welding process rather than the disclosed welding process, then the reflected laser beam is applied to the water-repellent resin and the reinforcing resin layer before falling on the capacitor component itself. However, since the water-repellent resin and the reinforcing resin layer serve the respective purposes of repelling water and reinforcing the capacitor component, it is unavoidable for the reflected laser beam to adversely affect the capacitor component itself, lowering the quality of the capacitor component itself.
It is therefore an object of the present invention to provide a chip capacitor of increased quality and a method of manufacturing such a chip capacitor.
According to the present invention, there is provided a chip capacitor comprising a capacitor component having an anode lead, a sintered body of a metal having a valve action in which the anode lead is embedded so as to project from an embedding surface, and a cathode conductor layer disposed on the sintered body, an anode terminal having a portion bent into a joint tongue, the anode lead being placed on the joint tongue, the joint tongue and the anode lead being welded to each other by a laser beam into an anode terminal, and an antireflection member for preventing the laser beam from being reflected, the antireflection member extending from a proximal end of the joint tongue of the anode terminal toward the sintered body.
The capacitor component comprises a resin-based insulating film layer containing a white pigment and disposed on the embedding surface of the capacitor component, and a water-repellent layer disposed on the resin-based insulating film layer. The capacitor component may comprise a water-repellent layer containing a white pigment and disposed on the embedding surface of the capacitor component.
The white pigment is contained in the resin-based insulating film layer preferably at a proportion ranging from 1 weight % to 85 weight %. The white pigment is contained in the water-repellent layer also preferably at a proportion ranging from 1 weight % to 85 weight %.
The water-repellent layer is preferably made of fluoroplastic with silicone resin added thereto.
The silicone resin is added preferably in a proportion ranging from 1 weight % to 40 weight %.
According to the present invention, there is also provided a method of manufacturing a chip capacitor, comprising the steps of:
a) shaping a powdery body of a metal having a valve action with a press, with an anode lead being embedded in powdery body and projecting from an embedding surface thereof, and sintering the shaped powdery body into an anode body;
b) producing a capacitor component by forming a resin-based insulating film layer containing a white pigment on the embedding surface of the anode body, thereafter forming a water-repellent layer on the resin-based insulating film layer, thereafter forming an oxide film on a surface of the anode body and then forming a semiconductor layer on the anode body, and thereafter forming a cathode conductor layer on the semiconductor layer;
c) placing the anode lead on a bent joint tongue and welding the joint tongue and the anode lead with a laser beam into an anode terminal; and
d) coating an upper surface of a placement plate of a cathode lead terminal with a conductive adhesive, and bonding the cathode conductor layer to the cathode lead terminal with the conductive adhesive, thus forming a cathode terminal.
According to the present invention, there is further provided a method of manufacturing a chip capacitor, comprising the steps of:
a) shaping a powdery body of a metal having a valve action with a press, with an anode lead being embedded in powdery body and projecting from an embedding surface thereof, and sintering the shaped powdery body into an anode body;
b) producing a capacitor component by forming a water-repellent layer containing a white pigment on the embedding surface of the anode body, thereafter forming an oxide film on a surface of the anode body and then forming a semiconductor layer on the anode body, and thereafter forming a cathode conductor layer on the semiconductor layer;
c) placing the anode lead on a bent joint tongue and welding the joint tongue and the anode lead with a laser beam into an anode terminal; and
d) coating an upper surface of a placement plate of a cathode lead terminal with a conductive adhesive, and bonding the cathode conductor layer to the cathode lead terminal with the conductive adhesive, thus forming a cathode terminal.
The step c) includes the step of providing an antireflection member for preventing the laser beam from being reflected, so as to extend from a proximal end of the joint tongue of the anode terminal toward the anode body, before the joint tongue and the anode lead are welded.
The step c) includes the step of providing an antireflection member for preventing the laser beam from being reflected, so as to extend from a proximal end of the joint tongue of the anode terminal toward the anode body, before the joint tongue and the anode lead are welded.
The step c) includes the steps of placing applying means for applying the laser beam, in a position forward in the direction in which the joint tongue extends, and applying the laser beam from the applying means to either one of the anode lead and the joint tongue, and blocking the laser beam with a shield member disposed between the applying means and the capacitor component and extending from a proximal end of the joint tongue of the anode terminal toward the anode body.
With the chip capacitor according to the present invention, the antireflection member for preventing the laser beam from being reflected extends from a proximal end of the joint tongue of the anode terminal toward the sintered body. When the joint tongue and the anode lead are welded to each other by a laser beam, the antireflection member prevents the laser beam which is not applied to the welded region, but is applied from the proximal end of the joint tongue of the anode terminal toward the sintered body, from being reflected. Therefore, the quality of the component body of the capacitor component is prevented from being lowered, making the chip capacitor higher in quality.
The resin-based insulating film layer containing the white pigment is disposed on the embedding surface of the anode lead of the sintered body, and the water-repellent layer is disposed on the resin-based insulating film layer. When the joint tongue and the anode lead are welded to each other by a laser beam, the resin-based insulating film layer containing the white pigment reflects a reflection of the laser beam from the welded region and blocks the reflection of the laser beam applied to the sintered body. Therefore, the quality of the component body including the sintered body is prevented from being lowered, making the chip capacitor higher in quality.
Since the water-repellent layer deposited on the resin-based insulating film layer which contains the white pigment serves as an outer surface, when the semiconductor layer is formed, the semiconductor mother liquor is reliably prevented by the water-repellent layer from creeping up the anode lead, thus reliably preventing the leakage current from increasing and the capacitor characteristics from being degraded. With the capacitor component protected against damage by being reinforced by the inner resin-based insulating film layer, the resin-based insulating film layer containing the white pigment and the water-repellent layer are successively formed on the embedding surface of the sintered body, so that the efficiency of the manufacturing operation can be increased and the production facility can easily be automatized.
If the water-repellent layer containing the white pigment is disposed on the embedding surface of the anode lead of the anode body, the quality of the component body including the sintered body is prevented from being lowered, making the chip capacitor higher in quality.
Since the proportion of the white pigment in the resin-based insulating film layer is in the range from 1 weight % to 85 weight %, when the joint tongue and the anode lead are welded to each other by the laser beam, a reflection of the laser beam from the welded region is reliably reflected by the layer containing the white pigment against being applied to the sintered body. Therefore, the quality of the component body including the sintered body is reliably prevented from being lowered, making the chip capacitor higher in quality.
Because the water-repellent layer is preferably made of fluoroplastic with silicone resin added thereto, its wettability is lowered. When the water-repellent layer is applied, therefore, it stays in the applied region and clearly indicates its presence. Specifically, if the water-repellent layer is made of fluoroplastic only, its wettability is so high that it does not stay in the applied region and the applied region cannot easily be identified. The present invention is effective to solve these problems. Further,as the added amount of silicone resin in water-repellent layer is in the range from 1 weight % to 40 weight %, the wettability of water-repellent layer is reliably low. When water-repellent layer is applied, it stays well in the applied region and clearly indicates its presence.
In the method of manufacturing a chip capacitor according to the present invention, the capacitor component is produced by forming a resin-based insulating film layer containing a white pigment on the embedding surface of the anode body, and thereafter, forming a water-repellent layer on the resin-based insulating film layer. The anode lead is placed on the joint tongue and the joint tongue and the anode lead are welded by a laser beam into an anode terminal. When the joint tongue and the anode lead are welded, the resin-based insulating film layer containing the white pigment reflects a reflection of the laser beam from the welded region, and prevents the reflection from being applied to the sintered body. Therefore, the quality of the component body including the sintered body is reliably prevented from being lowered, making the chip capacitor higher in quality.
When a semiconductor layer is formed after the resin-based insulating film layer and the water-repellent layer are formed, since the water-repellent layer has been formed on the resin-based insulating film layer containing the white pigment, the water-repellent layer serves as an outer surface, preventing the semiconductor mother liquor from creeping up the anode lead, thus reliably preventing the leakage current from increasing and the capacitor characteristics from being degraded. With the leakage current prevented from increasing and the capacitor characteristics prevented from being degraded and the capacitor component protected against damage by being reinforced by the inner resin-based insulating film layer, the resin-based insulating film layer and the water-repellent layer are successively deposited on the same embedding surface of the anode lead of the sintered body, so that the efficiency of the manufacturing operation can be increased and the production facility can easily be automatized.
In the above method, the antireflection member for preventing the laser beam from being reflected extends from the proximal end of the joint tongue of the anode terminal toward the sintered body. When the joint tongue and the anode lead are welded to each other by a laser beam applied from the area forward of the tip end of the joint tongue, the antireflection member prevents the laser beam which is applied from the proximal end of the joint tongue of the anode terminal toward the sintered body, from being reflected. Therefore, the reflection from the proximal end of the joint tongue of the anode terminal toward the sintered body is prevented from being applied to the component body including the sintered body. Therefore, the quality of the component body is reliably prevented from being lowered, making the chip capacitor higher in quality.
The shield member for blocking the laser beam applied from the proximal end of the joint tongue of the anode terminal toward the sintered body is disposed between the applying means and the capacitor component. The shield member blocks the laser beam from the area forward of the tip end of the joint tongue, which is not applied to the welded region, but applied from the proximal end of the joint tongue of the anode terminal toward the sintered body. The shield member thus prevents a reflection from this region from being applied to the component body including the sintered body. Consequently, the quality of the component body is reliably prevented from being lowered, making the chip capacitor higher in quality.
The above and other objects, features, and advantages of the present invention will become apparent from the following description based on the accompanying drawings, which illustrate examples of preferred embodiments of the present invention.